The present invention relates to a method and system for paying vendors for goods and/or services by means of a portable data medium comprising a memory and a control unit. Data are stored in the memory which preferably represent amounts of money or number of value units. In order to write such data representing total amounts of money or units available, the user establishes an operative connection with a crediting terminal through a data carrier, for example the user's bank through a connection via electrical contacts or in a contactless manner. Such connection can, for example, be via an electrical or other contactless means. The terminal initiates a writing process and debits the account of the user for the appropriate amount while crediting the user's data medium. Examples of the data medium are check cards, debit cards, and the like. This corresponds to withdrawing cash from the bank, with the difference that the cash now is directly available to the user not in the form of bank notes but as "electronic money". If the user wants to avail himself of a product from a vendor, for example for the purchase of goods or the use of a service, the user establishes a connection between his data medium and the vendor terminal. This can also take place via contacts or in a contactless manner. The vendor terminal than debits the amount of money or value unit or units corresponding to the desired product or service from the memory of the data medium and simultaneously credits the account of the vendor with this amount, preferably transferring it to a memory in the vendor terminal. The transition of the electronic money can take place as anonymously as the handing-over of bills, i.e. the memory of the vendor stores only the amounts of money, not however, information about the data medium from which the individual amounts of money have originated. This anonymity is due to the need for data security and privacy for the user.
When moving electronic money from the user's data medium into the memory of the vendor terminal, the amount of the money or units which are to be transferred, must be indicated. This takes place conventionally through fixed standard amounts, such as, for example, in vending machines or automatic ticket machines or ticket cancelers or by entering the amount, for example, using keys on the vendor terminal, which is carried out by the vendor. It is, in principle, possible for the vendor to enter a higher amount than that authorized by the user or holder of the card or medium, i.e. the customer. It is also possible for the terminal to be manipulated by the vendor in such a way that a higher amount is actually transferred from the data medium than is, for example, displayed at the vendor terminal. This can not practically be checked by the user of the data medium and subsequent proof is only possible in very involved ways. This causes uncertainties in the mind of the user when using the medium and differs from the case in which a product is paid for with cash. This represents a significant disadvantage when using electronic money.
U.S. Pat. No. 4,859,837 discloses a portable data medium comprising several separate memories from which amounts of money can be transferred to the outside with the memories being allocated to different accounts of the medium user. Transferring an amount of money to the outside is, however, only possible if previously a secret number has been entered into the medium by the user. Only one of the memories is not allocated to an account and accessible from the outside without entering a secret number. This known medium comprises a battery and further a display unit and buttons with which a secret number and also an amount of money can be entered in order to transfer this amount from one of the memories that is protected by the secret number, to the outside or into the unsecured memory. Due to the battery, the display unit and the buttons, the data medium can hardly be as small as a check card or other like medium. The data medium cannot be produced in a cost-effective manner, and the various possibilities of debiting from one of the memories requires a cumbersome operation and a complicated control.
German patent document DE 44 41 413 A1 describes a data exchange device with portable data medium comprising a memory for storing an amount of money. From this memory amounts of money can only be deducted after a secret number has previously been entered. Only payment of relatively small amounts of money is possible without a secret number and the maximum sum of the deductible relatively small amounts of money is defined. An unauthorized user who does not know the secret number can thus use only this maximum sum of money so that the damage is limited. The maximum sum, however, is defined in the data medium so that it cannot be changed and for meaningful use it cannot be selected to be so low such that when an incorrect, e.g. higher amount is deducted, noticeable damage still occurs to the legitimate owner. The use of an additional money memory in the medium, from which amounts of money can be deducted without a secret number thus, for various reasons, is not practical.
A system by the name MONDEX is known, in which a user has an electronic device in the approximate form of a wallet. The device comprises a display and a relatively large number of buttons as well as a memory. In this memory data representing amounts of money are stored. The electronic wallet further comprises a receiver for a portable data medium in the form of a chip card which also includes a memory. After the data medium is inserted into the receiver of the wallet, a selectable amount of money can be deducted from the memory of the device through the actuation of buttons and transferred into the memory of the data medium. The data medium can be used like cash if the vendor has a corresponding terminal with which amounts of money can be deducted from the data medium. If the wallet in which relatively large amounts can be stored, is, for security reasons, kept at a selected location, for example in the home of the user or owner, a greater amount of money is customarily transferred into the data medium than is required for paying for a single product. For that reason, this system represents an uncertainty for the user with respect to an erroneously or fraudulently acting vendor, just as in the case of a check card into which amounts of money are directly transferred from a bank in the form of data. The MONDEX system is furthermore cumbersome to handle.